Shaft for golf club with overlapped joint

ABSTRACT

The present invention provides a shaft for a golf club which is constructed such that overlapped joints are formed therein, thus providing effects of increasing the distance that a golf ball is driven, and of preventing the shaft of the golf club from momentarily twisting. To achieve the above-mentioned purpose, the shaft of the present invention includes an inner layer ( 110 ), which is provided at an innermost position, a middle layer ( 120 ), which is laminated around the circumferential outer surface of the inner layer, and an outer layer ( 130 ), which is laminated around the circumferential outer surface of the middle layer. The middle layer comprises a plurality of middle layer sheets, which are arranged in a longitudinal direction of the golf shaft such that the middle layer sheets partially overlap each other to form overlapped joints.

TECHNICAL FIELD

The present invention relates, in general, to shafts for golf clubshaving overlapped joints and, more particularly, to a shaft for a golfclub having overlapped joints, which provide effects of increasing thedistance that a golf ball is driven and of preventing the shaft of thegolf club from being momentarily twisted when impact energy is appliedfrom the golf club head to the golf ball.

BACKGROUND ART

Generally, a shaft for a golf club is manufactured through an innerlayer forming step of winding a double-layered sheet, which hasbias-angled grains and determines the basic strength and weight of theshaft of the golf club, around the circumferential outer surface of amandrel, a step of forming a triangular subsidiary sheet on thecircumferential outer surface of the inner layer to increase thethickness and strength of a tip part of the shaft, a middle layerforming step of winding one or two sheets having straight grains aroundthe inner layer and the triangular subsidiary sheet, a step of formingan outer layer around the circumferential outer surface of the middlelayer in the same manner as that of the middle layer forming step, and astep of winding heat-shrink tape around the circumferential outersurface of the outer layer, baking it using a heat treatment furnace,and removing the mandrel.

In the case of the conventional method, because one kind of sheet havingconstant strength and elasticity is used in each layer, and constanttonnage is applied thereto, when the golf club, which is manufactured bycoupling a club head to the tip part and by coupling a handle, that is,a grip, to a butt part of the shaft, strikes a golf ball, a single kickpoint is formed, in other words, the shaft is bent and elasticallyreturned to its original state only at a single point. Therefore, toincrease the distance that the golf ball is driven and the directionalcontrollability, high strength, high elasticity and high tonnage ofcarbon fiber prepreg, which is very expensive, must be used to form eachlayer. This induces a problem of an increase of the cost ofmanufacturing the shaft.

If relatively low strength, elasticity and tonnage of carbon fiberprepreg is used to reduce the manufacturing cost, the restoring force,that is, the elasticity, for increasing the distance that a golf ball isdriven is unsatisfactory, and twist resistance is not ensured.Furthermore, in the conventional arts, typically, several sets of sheetsare used to increase the twist resistance of the shaft. However, thiscauses a problem of an increase in the weight of the shaft.

Meanwhile, as representative examples of conventional techniquespertaining to the present invention, there are techniques, which wereproposed in Korean Patent Registration No. 10-0654365, entitled“REINFORCING SHEET STRUCTURE FOR GOLF SHAFT”, in Korean PatentRegistration No. 10-0404713, entitled “METHOD OF BRAID FIBERREINFORCEMENT GOLF SHAFT USING IMPROVEMENT OF CARBON FIBER REINFORCEMENTGOLF SHAFT”, and in Japanese Patent Laid-open Publication No.2005-152613, entitled “GOLF CLUB SHAFT”. These conventional techniquesare regarded as being included in the specification of the presentinvention.

Particularly, in Japanese Patent Laid-open Publication No. 2005-152613,entitled “GOLF CLUB SHAFT”, the shaft is constructed such that maximumbending rigidity points are formed at several positions and reducedbending rigidity regions are formed between the maximum bending rigiditypoints. Thus, the shaft bends consistently along the entire length ofthe shaft, and the head speed of the golf club is increased, thusincreasing the distance that a golf ball is driven. To achieve theabove-mentioned purpose, several sheets of prepreg having straightgrains are arranged in the longitudinal direction of the shaft. However,this technique is constructed such that the prepreg sheets merelycontact each other, and do not form overlapped joints.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a shaft for a golf club which is constructedsuch that overlapped joints are formed therein, thus providing effectsof increasing the distance that a golf ball is driven, and of preventingthe shaft of the golf club from being momentarily twisted when impactenergy is applied from the golf club head to the golf ball.

Technical Solution

In order to accomplish the above object, the present invention providesa shaft for a golf club having an overlapped joint, including an innerlayer provided at an innermost position, a middle layer laminated arounda circumferential outer surface of the inner layer, and an outer layerlaminated around a circumferential outer surface of the middle layer,wherein the middle layer comprises a plurality of middle layer sheetsarranged in a longitudinal direction of the golf shaft such that themiddle layer sheets partially overlap each other to form an overlappedjoint.

Preferably, a joint protrusion may be formed on a circumferential outersurface of the shaft of the golf club by the overlapped joint.

Furthermore, each of the middle layer sheets may differ from an adjacentmiddle layer sheet in one or more of strength, elasticity and tonnageapplied thereto.

In addition, the overlapped joint may be formed in a directionperpendicular to the longitudinal direction of the golf shaft.

As well, the overlapped joint may be formed in a direction inclined withrespect to the longitudinal direction of the golf shaft.

The middle layer may include a first middle layer having an overlappedjoint inclined upwards with respect to the longitudinal direction of thegolf shaft, and a second middle layer having an overlapped jointinclined downwards with respect to the longitudinal direction of thegolf shaft.

The inner layer may be formed by laminating double-layered sheets, eachof which has grains angled at a predetermined bias.

Preferably, a triangular subsidiary sheet, which is made of carbon fiberprepreg, may be wound between the inner layer and the middle layer toreinforce a shaft tip.

Furthermore, the middle layer may be formed by laminating at least onesheet of carbon fiber prepreg having grains oriented in a longitudinaldirection.

In addition, heat-shrink tape may be wound around a circumferentialouter surface of the outer layer.

Advantageous Effects

The shaft for golf clubs according to the present invention isconstructed such that overlapped joints, that is, joint protrusions, areformed therein, thus providing effects of increasing the distance that agolf ball is driven, and of preventing the shaft of the golf club frombeing momentarily twisted when impact energy is applied from the golfclub head to the golf ball.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a shaft for a golf club, according to anembodiment of the present invention;

FIG. 2 is a sectional view taken along the line A-A of FIG. 1;

FIG. 3 is views illustrating a method of manufacturing the shaft for thegolf club of FIG. 1;

FIG. 4 is a sectional view showing a middle layer of FIG. 3;

FIG. 5 is views illustrating a method of manufacturing a shaft for agolf club, according to another embodiment of the present invention; and

FIG. 6 is a perspective view of the shaft for the golf club,manufactured by the method of FIG. 5.

DESCRIPTION OF THE ELEMENTS IN THE DRAWINGS

-   1: tip part 2: butt-   3: joint protrusion-   10: mandrel 110: inner layer-   111: triangular subsidiary sheet-   120: middle layer 121: first middle layer-   122: second middle layer-   130: outer layer-   131: rectangular subsidiary sheet

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the construction and operation of embodiments of thepresent invention will be described in detail.

FIG. 1 is a perspective view of a shaft for a golf club, according to anembodiment of the present invention. FIG. 2 is a sectional view takenalong the line A-A of FIG. 1. FIG. 3 is views illustrating a method ofmanufacturing the shaft for the golf club of FIG. 1. FIG. 4 is asectional view showing a middle layer of FIG. 3.

As shown in FIG. 1, the shaft for the golf club according to theembodiment of the present invention includes a shaft tip 1, which isprovided on the upper end of the shaft for coupling a club head thereto,and a butt 2, which is provided on the lower end of the shaft forcoupling a grip, which is a handle, thereto. Furthermore, four jointprotrusions 3 are formed on the shaft such that kick points can beformed at three positions P1, P2 and P3. A method of forming the jointprotrusions 3 will be explained with reference to FIG. 3.

A mandrel 10 is a mold used to manufacture the shaft for the golf club.

All of an inner layer 110, middle layers 120 and an outer layer 130,which will be described below, are made of carbon fiber prepreg.

The inner layer 110 is a double-layered sheet, each layer of which hasgrains oriented at predetermined bias angles, for example, 30°, 35°,40°, 45°, etc., and the layers of which overlap each other such that thegrains thereof cross, thus forming an X shape. The inner layer 110 isformed by winding one or more double-layered sheets around the mandrel,and determines the flex and the weight of the shaft.

A triangular subsidiary sheet 111, which has straight grains oriented inthe longitudinal direction of the golf shaft, is wound around thecircumferential outer surface of the inner layer 110 to enhance thestrength, elasticity and durability of the shaft tip 1 and to set thethickness of the shaft such that it is suitable for the size of aninsert coupling part of the club head.

Here, each grain of the triangular subsidiary sheet 111 may be orientedat an angle perpendicular to the shaft or at other various angles, aswell as at a longitudinal angle.

In this embodiment, the middle layer 120 comprises a first middle layer121 and a second middle layer 122. Depending on the weight and flex ofthe shaft, or depending on the intended purpose, for example, dependingon whether the user is a man or a woman, one or more middle layers 120are used.

Furthermore, in this embodiment, to form the first middle layer 121,five middle layer pieces s1, s2, s3, s4 and s5 are arranged in thelongitudinal direction of the golf shaft such that the parts thereofoverlap each other to form four overlapped joints j1, j2, j3 and j4.

Each of the middle layer pieces s1, s2, s3, s4 and s5, which constitutethe first middle layer 121, is made of material having straight grainsoriented at a longitudinal angle. The middle layer pieces s1, s2, s3, s4and s5 differ from each other in strength, elasticity and tonnage.Furthermore, as shown in FIG. 4, the middle layer pieces s1, s2, s3, s4and s5 partially overlap each other, so that the overlapping parts formthe respective overlapped joints j1, j2, j3 and j4. The overlappedjoints j1, j2, j3 and j4 form respective joint protrusions 3 of the golfshaft, which is the final product.

The second middle layer 122 is manufactured through the same process asthat of the first middle layer 121.

The outer layer 130 is wound around the circumferential outer surface ofthe middle layer 120 and is made of one kind of material, which hasgrains oriented at an angle parallel to the longitudinal direction ofthe golf shaft and has strength, elasticity and tonnage appropriate forpreventing the overlapped joints j1, j2, j3 and j4 of the middle layer120 from being separated from each other when executing a golf swing andto ensure sufficient durability of the golf shaft. The outer layer 130comprises one or more sheets.

A rectangular subsidiary sheet 131 is wound around the circumferentialouter surface of the outer layer 130 to enhance the strength, elasticityand durability of the shaft and to set the thickness of the shaft suchthat it is suitable for the size of the insert coupling part of the clubhead, in the same manner as that of the triangular subsidiary sheet 111.The grains of the rectangular subsidiary sheet 131 may be oriented atvarious angles, for example, at an angle parallel to or perpendicular tothe longitudinal direction of the golf shaft.

Thereafter, processes of winding heat-shrink tape, conducting thermaltreatment, and removing the mandrel are conducted, in the same manner asin the conventional art.

FIG. 5 is views illustrating a method of manufacturing a shaft for agolf club, according to another embodiment of the present invention.FIG. 6 is a perspective view of the shaft for the golf club manufacturedby the method of FIG. 5.

The manufacturing process of this embodiment remains the same as that ofFIG. 3, excluding the middle layer 120.

In this embodiment, middle layer sheets s1, s2, s3, s4 and s5 are cut atinclined angles such that the inclined ends thereof have widths r1, r2,r3 and r4. Thereafter, the middle layer sheets s1, s2, s3, s4 and s5 arepartially overlapped with each other such that overlapped joints j1, j2,j3 and j4 are formed.

Preferably, the direction in which the ends of middle layer sheets of afirst middle layer 121 are inclined is opposite that of the secondmiddle layer 122, thus further enhancing the durability of the golfshaft.

In the case where the golf shaft is manufactured through this process,joint protrusions 3 having widths r1, r2, r3 and r4 are formed, as shownin FIG. 6. In other words, the width of each joint protrusion 3 of FIG.6 is markedly greater than that of the overlapped joint 3 of FIG. 1.

As such, in the case where the overlapped joints are formed in themiddle layer or the joint protrusions are formed in the shaft by theoverlapped joints, the following effects are achieved.

1) Multiple kick points (multiple joints) are formed in the shaft by thejoint protrusions, so that the inertial moment is increased such thatalmost all of the swing energy of a golfer can be converted to kineticenergy, thus increasing the distance that a golf ball is driven.

2) Because the overlapped joints, that is, the joint protrusions, arerelatively thick compared to other portions, they serve to prevent theshaft from momentarily twisting, in other words, to restrain the shaftwhen impact energy is applied from the golf club head to the golf ball.This restraining effect reduces the momentary twisting force when impactenergy is applied, such that the golf club head can strike the golf ballin a state of being parallel therewith, thus increasing the size of thearea of the club head that can be used to strike the golf ball, andenhancing the directional controllability. Furthermore, in the golfgame, which is a mental sport, the present invention makes it possiblefor the golfer to maintain psychological stability.

3) The clutch effect of the multiple kick points (multiple joints) andthe joint protrusions increases the momentary restoring force of theshaft, thus preventing the loss of swing energy. Furthermore, the clutcheffect generates energy over a wide area and disperses impact, thusreducing the impact applied to the golfer, thereby preventing the golferfrom being injured.

Although the preferred embodiments of the present invention have hasbeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible. Furthermore, the modifications, additions and substitutionsmust be regarded as falling within the bounds of the present invention,so long as they do not depart from the scope and spirit of theinvention.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides effects of increasingthe distance that a golf ball struck by a golf club is driven, and ofpreventing a shaft of the golf club from momentarily twisting.

1. A shaft for a golf club having an overlapped joint, comprising aninner layer provided at an innermost position, a middle layer laminatedaround a circumferential outer surface of the inner layer, and an outerlayer laminated around a circumferential outer surface of the middlelayer, wherein the middle layer comprises a plurality of middle layersheets arranged in a longitudinal direction of the golf shaft such thatthe middle layer sheets partially overlap each other to form anoverlapped joint.
 2. The shaft for the golf club according to claim 1,wherein a joint protrusion is formed on a circumferential outer surfaceof the shaft of the golf club by the overlapped joint.
 3. The shaft forthe golf club according to claim 1, wherein each of the middle layersheets differs from an adjacent middle layer sheet in one or more ofstrength, elasticity and tonnage applied thereto.
 4. The shaft for thegolf club according to claim 1, wherein the overlapped joint is formedin a direction perpendicular to the longitudinal direction of the golfshaft.
 5. The shaft for the golf club according to claim 1, wherein theoverlapped joint is formed in a direction inclined with respect to thelongitudinal direction of the golf shaft.
 6. The shaft for the golf clubaccording to claim 5, wherein the middle layer comprises a first middlelayer having an overlapped joint inclined upwards with respect to thelongitudinal direction of the golf shaft, and a second middle layerhaving an overlapped joint inclined downwards with respect to thelongitudinal direction of the golf shaft.
 7. The shaft for the golf clubaccording to claim 1, wherein the inner layer is formed by laminatingdouble-layered sheets, each of which has grains angled at apredetermined bias.
 8. The shaft for the golf club according to claim 1,wherein a triangular subsidiary sheet is wound between the inner layerand the middle layer to reinforce a shaft tip, the triangular subsidiarysheet being made of carbon fiber prepreg.
 9. The shaft for the golf clubaccording to claim 1, wherein the middle layer is formed by laminatingat least one sheet of carbon fiber prepreg having grains oriented in alongitudinal direction.
 10. The shaft for the golf club according toclaim 1, wherein heat-shrink tape is wound around a circumferentialouter surface of the outer layer.